In a closing method, a work piece constituted by a metal pipe material is rotated and a die is pressed against the work piece while the work piece is heated. Thus, the work piece undergoes plastic deformation as it gradually approaches the die.
A closing machine used in the closing operation comprises an outer diameter chuck that grips an outer peripheral surface of the work piece, and a chuck spindle that drives the outer diameter chuck to rotate together with the work piece. The outer diameter chuck grips the work piece, which is introduced via a conveyor or the like, and drives the work piece to rotate in a predetermined position. The closing machine presses a rotating die against the rotating work piece using the outer diameter chuck, and as a result, the work piece is closed into a predetermined shape corresponding to the die.
The closing method and closing machine described above are disclosed in JP2002-153930.
However, in this conventional closing machine, the processing precision of the work piece is determined according to the positional precision with which the chuck spindle holds the work piece, and therefore, if variation occurs in the positional precision with which the chuck spindle holds the work piece, the processing precision of the work piece deteriorates, making it difficult to close the work piece into a predetermined shape.
It is therefore an object of this invention to provide a closing method and a closing machine capable of improving the processing precision of a work piece without being affected by the positional precision with which a chuck spindle holds the work piece.